“Carrying Capacity”, “Overpopulation” and Environmental Degradation

by Nicholas Hildyard, Sarah Sexton and Larry Lohmann

first published 31 May 1993

Summary

The term “carrying capacity” was originally derived from the biological sciences, where it was used to denote the optimum number of a given species that a specific ecosystem could sustain without interfering with its basic structure and stability. In the context of people and the planet, the concept provides a seemingly “objective” measure of how many people can survive or flourish on a particular area of land at particular levels of consumption and technology. But far from being a neutral and objective measure of ecological stress, “carrying capacity” is being used as a means of preventing radical social change and of removing the concept of “overpopulation” from the realm of moral criticism and debate.

Contents

The term "carrying capacity" originally derived from the biological sciences, where it was used to denote the optimum number of a given species that a specific ecosystem is able to sustain without interfering with its basic structure and stability. For global managers, it is a concept that has a particular appeal since it provides a seemingly "objective" measure of how many people can survive or flourish on a particular area of land at particular levels of consumption and technology. If "carrying capacity" is exceeded, the reasoning goes, then population can be said to be "objectively" excessive relative to land, consumption and technology.

It is not as easy as all that, however, to remove the concept of "overpopulation" from the realm of moral criticism and debate. Outsiders' claims that a given area of land has a certain "carrying capacity" are open to criticism in three different ways. First, the number of people who can live on a piece of land depends largely on their culture, which determines both their needs and their ways of life. The nature and success of their farming systems, for example, cannot easily be predicted in advance on the model of outsiders' cultures. Second, the fact that the question of consumption and technology levels must be raised in any discussion of "carrying capacity" means that the normative issues of what sort of society or economy people desire cannot be evaded when talking of "overpopulation". Third, a given land area's "carrying capacity" will depend largely on what happens outside its borders: upstream deforestation, global commodity price fluctuations, greenhouse gas emissions, acid rain and so forth. Local inhabitants will always be justified in pointing out that their land could support a great many more people if damaging external influences were curbed, and on this ground to call into question the presumption of those partly responsible for such influences in suggesting "proper" local population levels.

This latter problem might be evaded, of course, by an attempt to determine global carrying capacity. However, this is usually acknowledged to be technically far-fetched even if the world's peoples could be induced to accept uniform global consumption levels and technology. And it would of course leave wide open the question of which local "populations" would have to be "adjusted" to meet the purported "global" requirements.

One response to such arguments is that, while "overpopulation" cannot be precisely or "objectively" defined, there are at least unambiguous statistical correlations between "population" and environmental degradation on a national scale. On close examination, however, even this assertion turns out to be problematic. Malaysia, for example, although it has only a tenth as many people as neighbouring Indonesia, has cleared fully 40 per cent as much forest as Indonesia has done. Central America, with a "population" density of only 57 persons per square kilometre, has cleared 410,000 square kilometres of forests, or 82 per cent of its original forest cover, while France, covering the same land area with double the number of people, has cleared less. And those who would explain the destruction of half a million square kilometres of Brazilian Amazonian forests between 1975 and 1988 in Malthusian terms "overlook the inconvenient fact that although the Amazon forms over 60 per cent of Brazilian national territory, less than 10 per cent of Brazil's population lives there..."

If "population" and "population" density are poorly correlated with specific examples of environmental degradation, "population" increase is equally poorly correlated with rates of environmental degradation. Costa Rica and Cameroon, for example, are clearing their forests faster than Guatemala and Zaire, respectively, in spite of having lower "population" growth rates. Thailand's rate of forest encroachment, similarly, has varied less closely with the rate of population increase than with changes in political climate, villagers' security, road and dam-building, and logging concessions.

To confuse the issue still further, there are many instances of environmental degradation resulting from the outflow of people from a given area of land. In Africa, for example, there are many areas where fallow periods have been reduced, not because there is a shortage of land, due to "population pressure", but because there is a shortage of farm labour due to urban migration. The longer a plot of cleared bush is left fallow, the more labour is required to clear it again for agriculture: hence, it makes economic (if not ecological) sense to reduce the fallow period. In such cases, the problems associated with reduced fallow periods result not from overpopulation but from local depopulation.

Indeed, the closer one looks at the relationship between human numbers and environmental degradation, the clearer it becomes that, at root, the key issue is not simply how many? but how is society organized? In the case of deforestation, for example, the periods of most rapid destruction "have not necessarily been at the times when population was most rapidly expanding. They have occurred when the exploitation of subordinate groups (as well as of resources) has intensified". The halving of Central America's forest area between 1950 and 1990, for example, is due not to a "population explosion" but to the concentration of land in the hands of a limited number of rich ranchers and landowners raising bananas, cotton, coffee and cattle. Peasants have been used as land-clearers only to be pushed into the hills, where they displace others and are forced to cut yet more forest. Elsewhere, transnational corporations such as Finland's Jaakko Pöyry Oy, the US's Scott Paper, and Japan's Marubeni often supervise forest plunder, with additional destruction resulting from expropriative cattle-raising, road, hydro-electric and industrial projects.

In the Amazon, most land cleared of forest produces little in the way of food and often was not cleared for that purpose. Migration into the forests has much more to do with structural changes in the regions of emigration than with "population" growth. Thus, decline in access to land, as it occurred in North-Eastern Brazil, stimulated emigration. In the case of migrants from the South of Brazil, the expansion of mechanized agriculture and the flooding of enormous areas of agricultural land forced small farmers out of their holdings. Finally, the threat of violence and lack of employment have also expelled farmers from their holdings. Since more than half of all agriculturalists in Brazil rely on wage labour as well as cropping for their income, activities like mechanization which reduce rural employment are often as disastrous to peasants as brute expulsion from their lands.

For those who would avoid such issues, the concept of "carrying capacity" offers a welcome life-belt. Seemingly objective, it depoliticises what is a highly political issue by reducing the debate to one of mathematics. In its recommendations to the 1992 UN Conference on Environment and Development (UNCED) on sustainable agriculture, for example, the UN Food and Agriculture Organization (FAO) argues that governments should "evaluate the carrying and population supporting capacity of major agricultural areas", and, where such areas are to deemed to be "overpopulated", take steps to change "the man/land ratio" (sic) by "facilitating the accommodation of migrating populations into better-endowed areas". Elsewhere, FAO is more candid, specifically recommending "transmigration" programmes. Peasants who have been forced onto marginal lands as a result of the best quality land being taken over for intensive export-oriented agriculture may thus be liable to resettlement because officials calculate that they are a threat to local "carrying capacity": yet, nowhere in its Sustainable Agriculture and Rural Development policy paper does FAO consider the alternative option that ecological stress in marginal areas might be better relieved by reclaiming the best farm land for peasant agriculture. In effect, far from being a neutral and objective measure of ecological stress, carrying capacity is already being used as a means of preventing radical social change.